Forces Flashcards
Define a newton
Force causing 1kg of mass to accelerate 1ms⁻²
Define density
Mass per unit volume of a substance
Define pressure
The force exerted per unit cross sectional area
Define pascal
Is 1 newton per square meter
Define torque of a couple
The turning effect of a couple
Define centre of mass
A point which external forces produce a straight line motion but no rotation
Define weight
The gravitational force on an object
What is Archimedes principle
Upward force is equal to the weight of the fluid it displaces
Define terminal velocity
The constant speed reached when drag force is equal
Define moment
The turning effect of a force
Define centre of gravity
A point where weight if an object appears to act
How do you find the centre of gravity
- Make holes along the edges of the object and let it hang freely from a pin
- It will come to rest with its centre of gravity below the pin
- Hang a plumb line from the pin and draw a line along the plumb line
- Repeat this for the other holes
- Where the lines intersect is the centre of gravity
Define drag
It is the frictional force that opposes the motion of the object
What does drag depend on
- Density of fluid
- Shape
- Speed
The two most important factors are speed and cross sectional area
Determining terminal velocity in fluids
- Put elastic bands around the tube of viscous liquid in fixed distances
- Drop a ball bearing and record the time at which it reaches each band
- Repeat this a few times to reduce random errors
- Calculate time take by the ball to travel between each band and find the velocity
What are the principle in moments
When a body is in equilibrium the net force acting on it is zero and it’s net movement is 0.
The sum of clockwise moments = anti-clockwise moments
Moment= force x distance
What is a couple
A pair of equal but opposite forces to the object
Equation for density
ρ= m/v (kgm⁻³)
Equation for pressure
P=F/a (Nm⁻²)
Equation for pressure in liquids
P=hρg
ρ=density of the liquid
Equation for upthrust
Upthrust= axρg
Equation for work done
W=Fx
What are the different types of energy
Kinetic Gravitational Chemical elastic potential Nuclear Radiant Sound Electrical potential Thermal
What is kinetic energy
Is energy due to the motion of an object with mass
What is gravitational potential energy
Energy due to its position in a gravitational field
What is chemical energy
Energy contained within bonds between atoms
What is elastic potential energy
Is energy stored in a object as a result of reversible change in its shape
What is electrical potential energy
Is energy of electrical charges due to their position in an electric field
What is nuclear energy
Is energy within the nuclei of an atom
What is radiant energy
Is energy oscillated with all electromagnetic waves, stored within the oscillating electric and magnetic fields
What is sound energy
Is energy of mechanical waves due to the movement of atoms
What is thermal energy
Is the sum of random potential and kinetic energies of atoms in a system
Equation for kinetic energy
Ek=0.5mv²
W=Fd F=ma
W=mad v²=u²+2as
W=m x v²/2s x d s and d cancel
What is the equation for GPE
Ep=mgh
W=Fd F=weight
W=mgh
Equations for power
P=w/t
P=fv v=velocity
P=w/t = fx/t (x/t)=velocity
Define displacement
Distance traveled in a particular direction
Define instantaneous speed
The speed at the moment it’s measured
Define average speed
The rate of change in distance calculated over a complete journey
Define Accelerated
The rate of change of velocity, a vector quantity
Define velocity
A vector quantity equal to the rate of change in displacement
What is thinking distance
The distance travelled between the moment when you first see a reason to stop
What is Breaking distance
Is distance traveled from the moment breaks where applied
Define moment
Force X perpendicular distance form the pivot to the line of action of the force
